基于多个条件通过 linq 过滤收集

Question

I have collection that i want to filter based on multiple criteria .

That's my filter class:

class CriteriaClass {
    public DertEnum? DertEnum { get; set; }
    public string UserName { get; set; }
    
    CriteriaClass() {
        DertEnum = null;
        UserName = string.Empty;
    }
}

My question is how to say here that if criteriaClass.DertEnum is null not to include it in linq filter. Same for criteriaClass.UserName if it's empty . How to use to not go into if/else. I am sure there is a way.

_data = new ObservableCollection<MyModel>(_data.Where(w =>
    (w.DertEnum.Equals(EnumTools.T(criteriaClass.WarehouseActionTypeEnum)))
    && (w.UserName.Equals(criteriaClass.UserName))));

Answer 1

To check if something is not null , you can use is object . To check if a string is null or empty, you can use String.IsNullOrEmpty() :

_data = new ObservableCollection<MyModel>(_data.Where(w => w.DertEnum is object
                                                           && !String.IsNullOrEmpty(w.UserName)
                                                           && (<your other criterias go there>)))

Answer 2

Add a logical or is null check to the where criteria:

_data = new ObservableCollection<MyModel>(_data.Where(w =>
    ((w.DertEnum is null || w.DertEnum.Equals(EnumTools.T(criteriaClass.WarehouseActionTypeEnum))))
    && (w.UserName.Equals(criteriaClass.UserName))));